Fastening friction plate, and fastening and fixing structure for strain wave gearing and output member

ABSTRACT

A fastening friction plate is wedged between the fastening surfaces of two fastening members in order to increase the fastening force between them. The fastening friction plate has a friction plate main body of a fixed thickness, and engaging protuberances having an approximately truncated cone shape formed on the both surfaces of the friction plate main body at a fixed pitch. The friction plate main body and the engaging protuberances are integrally formed by photo-etching into the both surfaces of a steel plate material having a fixed thickness. The hardness of the fastening friction plate is equal to or greater than that of the fastening surfaces of the fastening members.

TECHNICAL FIELD

The present invention relates to a fastening friction plate for use infixedly fastening a member for torque transmission, and a fastening andfixing structure for a strain wave gearing and an output memberutilizing the fastening friction plate.

BACKGROUND ART

One known example of a structure of fixedly fastening two members fortransmitting torque is a structure in which a friction plate is wedgedbetween the fastened surfaces of the two members being fastened, and thetwo members are fixed in a fastened manner by a bolt or the like. PatentDocument 1 provides a friction sheet used in such a fastening and fixingstructure. In this friction sheet, the surface of a metal elastic sheetis plated with diamond grains that can dig into the fastening surfacesof the fastening-target member.

For example, when a friction sheet is wedged between the fastening endsurfaces of two shaft members and the fastening end surfaces are fixedin a fastened manner by a fastening bolt, the diamond grains on bothsides of the friction sheet dig into the fastening end surfaces of bothmembers and a large frictional force is produced between these fasteningend surfaces. The fastening force of the two shaft members therebyincreases, and a large torque can be transmitted.

PRIOR ART DOCUMENT Patent Document

-   [Patent Document 1] JP 3547645

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In a fastening and fixing structure that uses a friction sheet, diamondpowder retained by the plating layer may fall off. When the diamondgrains that have fallen off scatter and infiltrate places such as therotational sliding portions of the shafts to be fastened, these portionsmay be subjected to wear and damage.

For example, such a friction sheet as described above is considered tobe used for fix in a fastening matter the reduced rotation outputelement of a strain wave gearing with a load-side output shaft. When astrain wave gearing called as cup-type or silk-hat-type is employed, acup-shaped flexible externally toothed gear or silk-hat-shaped flexibleexternally toothed gear is commonly set to be the reduced rotationoutput element. A friction sheet is, for example, wedged between the endsurface of a discoid boss which defines the cup bottom portion of aflexible externally toothed gear and the end surface of an output shaft,and the output shaft is fixed in a fastening manner with the end surfaceof the boss with fastening bolts

In this case, diamond grains that have fallen off from the frictionsheet may infiltrate places such as sliding portions between theflexible externally toothed gear and the wave generator, and meshingportions between the flexible externally toothed gear and the rigidinternally toothed gear. When hard diamond grains infiltrate theseportions, these portions may be subjected to wear and damage.

In view of the above points, an object of the present invention is toprovide a fastening friction plate which prevents foreign matters fromproducing and which gives no damage to the side of a member to befastened.

Another object of the present invention is to provide a fastening andfixing structure for a strain wave gearing and an output member.

Means to Solve the Above Problems

To solve the problems described above, according to the presentinvention, there is provided a fastening friction plate wedged betweenfastening surfaces of two fastening members to be fixed together in afastening manner, the fastening friction plate characterized incomprising:

a friction plate main body having a predetermined thickness;

engaging protuberances of a predetermined size formed at a predeterminedpitch on both surfaces of the friction plate main body;

the friction plate main body and the engaging protuberances beingintegrally formed by photo-etching into both surfaces of a steel platematerial; and

a hardness being at equal to or great than a hardness of the fasteningsurface of the fastening members.

It is preferable that the engaging protuberances are taperingprotuberances protruding perpendicularly from the surface of thefriction plate main body, the tips of the engaging protuberances areflat peak surfaces parallel to the surface of the friction plate mainbody, and the cross-sectional shapes of the engaging protuberancesorthogonal to the direction of protrusion are circular, square, ortriangular. The engaging protuberances are preferably arranged in amatrix at constant pitches.

When the two fastening components are fastened and fixed together in amanner in which the fastening friction plate is wedged between them, theengaging protuberances formed on the both surfaces of the fasteningfriction plate dig into the fastening surfaces to produce a largefrictional force between the fastening surfaces. The engagingprotuberances are integrally photo-etched into the surfaces of the blankof the friction plate made of a steel plate. It is therefore possible toprevent or suppress adverse events such as the engaging protuberancesdetaching from the friction plate main body and infiltrating the slidingportions and other portions.

Next, a fastening and fixing structure for a strain wave gearing and anoutput member of the present invention is characterized in that:

a reduced rotation output element of the strain wave gearing and theoutput member to which the reduced rotation is transferred from thereduced rotation output member are fastened and fixed in a state inwhich a fastening friction plate is wedged therebetween;

the fastening friction plate has engaging protuberances of apredetermined size formed at a predetermined pitch on both side surfacesof the friction plate main body,

the friction plate main body and the engaging protuberances areintegrally formed by photo-etching into both surfaces of a steel platematerial; and

a hardness of the fastening friction plate is at least a hardness of thefastening surfaces of the reduced rotation output element and the outputmember.

Here, it is preferable that the engaging protuberances are taperingprotuberances protruding perpendicularly from the surface of thefriction plate main body, the tips of the engaging protuberances areflat peak surfaces parallel to the surface of the friction plate mainbody, and the cross-sectional shapes of the engaging protuberancesorthogonal to the direction of protrusion are circular, square, ortriangular.

The reduced rotation output element is generally a flexible externallytoothed gear, and the hardness thereof is HRC36 to HRC50 in general. Inthis case, the hardness of the fastening friction plate is preferablyequal to or greater than HRC55.

Further, in this case, it is preferable that:

the plate thickness of the friction plate main body is 0.1 to 0.5 mm;

the pitch of the engaging protuberances is 0.2 to 0.5 mm;

the maximum diameter or maximum width of the peak surfaces of theengaging protuberances is 0.01 to 0.05 mm; and

the height of the engaging protuberances is 1.0 to 1.2 times the maximumdiameter or maximum width of the peak surfaces of the protuberances.

In the consideration that the required transfer torque from a standardflexible externally toothed gear to an output member, a fastening forcebetween them, and the hardness of each of the fastening members, thesize, shape and pitch of the engaging protuberances are appropriatelyset, so that it is possible to make the engaging protuberances to diginto the fastening surfaces of the flexible externally toothed gear andthe output member by an appropriate dig-in depth. Whereby, a coefficientof friction of the fastening portion between the flexible externallytoothed gear and the output member can be made large. Thus, it ispossible to realize a fastening structure capable of transferring alarge torque.

Further, when the size, shape and pitch of the engaging protuberancesare set as described above, it is preferable that the engagingprotuberances are arranged in a density of 40 to 250 per 10 mm².

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A perspective view of a cup-shaped strain wave gear reducer towhich the present invention is applied.

FIG. 2 A longitudinal cross-sectional view of the strain wave gearreducer.

FIG. 3 A longitudinal cross-sectional view showing the fastening andfixing structure for the boss of the flexible externally toothed gear ofthe strain wave gear reducer and a load-side output shaft.

FIG. 4 A longitudinal cross-sectional view showing the structuralcomponents of the fastening and fixing structure of FIG. 3 in adissembled state.

FIG. 5 A plan view showing the fastening friction plate.

FIG. 6 (a) is a partial enlarged plan view showing the fasteningfriction plate, (b) is a partial enlarged cross-sectional view, and (c)is a partial enlarged cross-sectional view.

FIG. 7 A schematic diagram showing the steps of manufacturing theengaging protuberances by photo etching.

FIG. 8 (a) is a partial enlarged plan view showing another example ofthe engaging protuberances of the fastening friction plate, (b) is apartial enlarged cross-sectional view, and (c) is a partial enlargedcross-sectional view.

FIG. 9 (a) is a partial enlarged plan view showing another example ofthe engaging protuberances of the fastening friction plate, (b) is apartial enlarged cross-sectional view, and (c) is a partial enlargedcross-sectional view.

FIG. 10 (a) is a schematic diagram showing a conic protuberance in astate of pressing into the surface of a steel material, and (b) is aschematic diagram showing an engaging protuberance in a state of digginginto the boss.

MODE FOR CARRYING OUT THE INVENTION

The following is a description, made with reference to the drawings, ofan embodiment of a fastening and fixing structure for a strain wave gearreducer and a load-side output shaft.

(Strain Wave Gear Reducer)

FIG. 1 is a perspective view showing a cup-type strain wave gearreducer, and FIG. 2 is a longitudinal cross-sectional view thereof. Thestrain wave gear reducer 1 comprises an annular rigid internally toothedgear 2, a cup-shaped flexible externally toothed gear 3 disposed insidethe rigid internally toothed gear 2, and an elliptically contoured wavegenerator 4 fitted inside the flexible externally toothed gear.

The cup-shaped flexible externally toothed gear 3 comprises acylindrical barrel part 5 capable of flexing in the radial direction, anannular diaphragm 6 extending inward from the rear end edge of thebarrel part, an annular boss 7 formed as a continuation of the innercircumferential edge of the diaphragm 6, and external teeth 8 formed inthe outer circumferential surface portion in the open end side of thecylindrical barrel part 5. The wave generator 4 is fitted into the innerside of the portion of the cylindrical barrel part 5 where the externalteeth 8 are formed in the flexible externally toothed gear 3. Thecylindrical barrel part 5 is made to flex into an ellipsoidalconfiguration, and the portions of the external teeth 8 positioned atboth ends of the major axis of the ellipsoidal configuration are meshedwith internal teeth 9 of the rigid internally toothed gear 2.

The wave generator 4 is fixedly connected with a rotating input shaft(not shown) such as a motor shaft, and is rotatably driven by thisrotating input shaft. When the wave generator 4 rotates, the meshingpositions of the gears 2, 3 move in the circumferential direction. As aresult, relative rotation occurs between the gears in accordance withthe difference in the number of teeth between the two gears. In thepresent example, the rigid internally toothed gear 2 is fixed to amember on the fixed side (not shown), and the flexible externallytoothed gear 3 constitutes a reduced rotation output element, from whichthe reduced rotation is outputted.

FIG. 3 is a longitudinal cross-sectional view showing the fastening andfixing structure between the flexible externally toothed gear 3 and theload-side output shaft, and FIG. 4 is a schematic diagram showing anexploded view of the structural components thereof. A load-side outputmember 11 is fastened and fixed to the annular boss 7 of the flexibleexternally toothed gear 3 in a manner in which a disc-shaped fasteningfriction plate 10 is wedged between them. A plurality of fastening bolts13 are used for this fastening and fixing.

A shaft-side flange 14 having a large diameter is formed in the rear endof the output shaft 11, and the circular rear end surface of theshaft-side flange 14 is a shaft-side fastening surface 15. Theshaft-side fastening surface 15 is superposed coaxially with a boss-sidefastening surface 16, which is the outer side end surface of the boss 7,in a manner in which the fastening friction plate 10 is wedged betweenthem. An attachment flange 12 is superposed coaxially with the innerside end surface of the boss 7. Bolt holes are formed at fixed intervalsin the circumferential direction in the shaft-side flange 14, and boltinsertion holes are similarly formed at fixed intervals in thecircumferential direction in the boss 7 and the attachment flange 12.The four members are coaxially superposed so that these bolt holes andbolt insertion holes coincide, and the four members are fixed in afastened manner with a predetermined bolt tension by the fastening bolts13 inserted from the side of the attachment flange 12.

FIG. 5 is a plan view showing the fastening friction plate 10, and FIG.6(a) to (c) are, respectively, a partial enlarged plan view showing anenlarged view of the surface of the boss-side fastening surface 16, apartial enlarged cross-sectional view sectioned along line b-b, and apartial enlarged cross-sectional view sectioned along line c-c.

The fastening friction plate 10 is constituted so that it comprises afriction plate main body 21 having a constant plate thickness and ashape corresponding to that of the boss-side fastening surface 16 (seeFIG. 4), a circular center through hole 22, and a plurality of boltinsertion holes 23 arranged at a constant interval along thecircumferential direction, the hole 22 and the insertion holes 23 beingformed in the friction plate main body.

One of the surfaces of the friction plate main body 21 is a boss-sidesurface 24 which is superposed on the boss-side fastening surface 16,and the other surface thereof is a shaft-side surface 25 which issuperposed on the shaft-side fastening surface 15. These boss-side andshaft-side surfaces 24, 25 are integrally formed with engagingprotuberances 26, 27 of a predetermined shape at a fixed pitch by photoetching.

The friction plate main body 21 of the present embodiment has a platethickness of 0.1 to 0.5 mm. The engaging protuberances 26, 27 arearrayed in a matrix at fixed pitches, and the pitches Pa(x), Pa(y), Pb(x) and Pb(y) of adjacent engaging protuberances each fall within arange of 0.2 to 0.5 mm. The arrayed pattern of the engagingprotuberances 26, 27 may be an arrayed pattern other than a matrixarrayed pattern. The arrayed patterns of protuberances for the boss-sideand shaft-side surfaces 24 and 25 can be those different with eachother.

The engaging protuberances 26, 27 are protuberances having an overallshape resembling a circular truncated cone, and the center axis lines 26a, 27 a thereof are perpendicular to the friction plate main body 21.The outer circumferential surfaces 26 b, 27 b of the respective engagingprotuberances 26, 27 are formed from curved surfaces that taper towardsthe tip. The peak surfaces 26 c, 27 c of the engaging protuberances areflat circular surfaces orthogonal to the center axis lines 26 a, 27 a.

The maximum diameters La, Lb of the peak surfaces 26 c, 27 c in theengaging protuberances 26, 27 are 0.01 to 0.05 mm. The heights Ha, Hb ofthe engaging protuberances 26, 27 (which are heights from the boss-sidesurface 24 of the friction plate main body 21 and from the shaft-sidesurface 25) are equal to or less than 0.06 mm, and at the same time, 1.0to 1.2 times the maximum diameter L of the peak surfaces 26 c, 27 c. Theheights Ha and Hb can be either same to or different form each other.The engaging protuberances 26, 27 are also formed with a density of 40to 250 per 10 mm².

In the example depicted, the plate thickness T of the friction platemain body 21 is 0.1 mm, the diameters La, Lb of the peak surfaces 26 c,27 c of the engaging protuberances 26, 27 are 0.05 mm, the heights Ha,Hb are 0.065 mm, and the pitches Pa(x), Pa(y), Pb(x), Pb(y) are 0.2 mm.

The hardness of the friction plate main body 21 and the engagingprotuberances 26, 27 is HRC 55 or greater. A material having a hardnessof HRC55 or greater may be used as a blank of the fastening frictionplate. Otherwise, when the hardness of the blank is less than HRC55, asurface treatment such as a heat treatment, a carburizing treatment, ora nitriding treatment may be performed during either the stage before orthe stage after photo-etching the engaging protuberances 26, 27 to bringthe hardness of the both-side surfaces of the friction plat main body 21and the engaging protuberances 26, 27 to HRC55 or greater. The hardnessof the flexible externally toothed gear 3 is commonly between HRC36 to50, and the material hardness of the output member 11 is the same. Sincethe hardness of the fastening friction plate 10 is set greater thanthose of the flexible externally toothed gear and the output shaft, itis possible to make the engaging protuberances 26, 27 to dig into theboss-side fastening surface 16 and the shaft-side fastening surface 15by the fastening force (axial force) of the fastening bolts 13.

The engaging protuberances 26, 27 herein can be formed by commonphoto-etching. For example, as shown in FIG. 7, a blank 10A made ofsteel plate is prepared (FIG. 7(a)) and a photo resist film 31 is formedon the both surfaces of the blank (FIG. 7(b)). The photo resist film 31is then subjected to light exposure and image development to form amasking pattern on the photo resist film (FIG. 7(c)). Wet etching, forexample, is then performed on the exposed surface portions of the blank10A to form the engaging protuberances 26, 27 (FIG. 7(d)). The maskingpattern of the photo resist film 31 is then peeled off, and posttreatments such as washing and drying steps are performed (FIG. 7(e)).Substantially circular truncated cone-shaped engaging protuberances 26,27 in the case that the masking pattern is circular, are thereby formedintegrally in the both surfaces of the friction plate main body 21. Inthe case that the masking pattern is square or triangular, squaretruncated cone-shaped or triangular truncated cone-shaped engagingprotuberances 26, 27 are formed. Usually, the engaging protuberances areformed on one surface of the blank 10A and then are formed on the othersurface thereof.

FIGS. 8 and 9 show other shapes of the engaging protuberances 26, 27.The engaging protuberances 26A, 27A shown in FIG. 8 overall have asubstantially square truncated cone shape. For example, the peaksurfaces of the engaging protuberances 26A, 27A are regulartetrahedrons, the width is 0.05 mm, the height is 0.06 mm, and the pitchis 0.2 mm. The engaging protuberances 26B, 27B shown in FIG. 9 overallhave a substantially triangular truncated cone shape. For example, thepeak surfaces of the engaging protuberances 26B, 27 b are equilateraltriangles, and the width of these equilateral triangles is 0.06 mm. Theheight of the engaging protuberances 26B, 27B is 0.06 mm and the pitchis 0.2 mm. In every row of the engaging protuberances 26B, 27B arrayedin a matrix, every other triangle is reversed in orientation.

In the fastening and fixing structure between the flexible externallytoothed gear 3 and the load-side output shaft 11, the fastening forcewhen the engaging protuberances 26, 27 of the fastening friction plate10 dig into (press into) the boss-side fastening surface 16 and theshaft-side fastening surface 15 can be approximated as the wearassociated with digging out steel. To give a description referencingFIG. 10(a), a case is envisioned in which conic protuberances press intothe fastening surface. In this case, n conic protuberances are incontact with the fastening surface. The projected surface area(triangular) At of the conic protuberances in the advancing directionshown by the bold arrow is expressed by the following formula.At=n·r·d=n·r·r·cot θ=n·r2·(1/tan θ)

-   -   r: the average radius of the indentations made by the conic        protuberances    -   θ: half the apex angle of the conic protuberances    -   d: depth

The surface area of the indentations made by the conic protuberances canbe approximated as shown by the following formula.Surface area of indentations made by conic protuberances≈Real contactarea Ar=P/Pm=n·πr ²

-   -   P: total load    -   Pm: average surface pressure of real contact area

Therefore, with F being a dig-out resistance force (frictional force),the coefficient of friction μ can be expressed by the following formula.Coefficient of friction μ=F/P=At·Pm/Ar·Pm=At/Ar=1/(π·tan θ)When θ of the conic protuberances is 45 degrees, μ=0.3183.

FIG. 10(b) shows a case in which the circular truncated cone-shapedengaging protuberances 26, 27 of the present example are made to diginto the boss-side fastening surface 16 and the shaft-side fasteningsurface 15. In this case, the values can be approximated as follows.

Dig-in depth x≈d

Dig-in projected surface area AT≈At

Indentation surface area AR≈Ar

Approximate coefficient of friction M=AT/AR

The transmitted torque of the fastening and fixing structure using thefastening friction plate 20 is greatly affected by both coefficients offriction of the boss-side fastening surface 16 and the shaft-sidefastening surface 15 when the engaging protuberances 26, 27 are made todig into (press into) these fastening surfaces. These coefficients offriction can be defined by the dig-in projected surface area AT and theindentation surface area AR as stated above. Specifically, thecoefficients of friction are determined by the respective shapes, sizes,and dig-in depths of the engaging protuberances 26, 27, and by thedifferences in hardness between the fastening friction plate 20 andboss-side fastening surface 16 and between the fastening friction plate20 and the shaft-side fastening surface 15.

Therefore, fastening surfaces having the desired coefficient of frictioncan be obtained by appropriately setting the shapes and sizes of theengaging protuberances 26, 27, the hardness of the fastening frictionplate 20. In the present example, the circular truncated cone-shapedengaging protuberances 26, 27 are formed by photo etching (chemicaletching). Large coefficients of friction can be achieved by giving theengaging protuberances 26, 27 so shaped the size D of the peak surfaces,the protuberance height H, and the hardness described above.

The number of protuberances n is limited by the shear strength of thematerial as derived from the total indentation surface area (AR×n). Inthe present example, the number of protuberances n is 40 to 250 per 10mm², taking into account the shear strength of the fastening frictionplate 20.

Furthermore, when the same bolt tension is applied, the dig-in depth xof the engaging protuberances differs depending on the shape of the peaksurfaces of the protuberances. When the shape of the peak surfaces ofthe engaging protuberances is circular, square, and triangular, assumingall other conditions are equal, the triangular surfaces dig in the mosteasily, and the circular surfaces dig in with the most difficulty.Fastening surfaces of lower hardness have a greater dig-in depth x thanfastening surfaces of higher hardness. Furthermore, the dig-in depth xof the engaging protuberances differs depending on the surface area ofthe peak surfaces of the engaging protuberances, and surfaces of lesssurface area dig in more easily. Similarly, peak surfaces of theengaging protuberances having less total surface area dig in more easilythan peak surfaces having greater total surface area. Therefore, thesize and shape (the shape of the peak surfaces, the surface area, andthe protuberance height) of the engaging protuberances 26, 27, the pitchand number of engaging protuberances 26, 27 per unit surface area, andthe hardness of all components are preferably set as appropriateaccording to the size of the flexible externally toothed gear to befastened, the necessary transmitted torque, and the added tension.

The invention claimed is:
 1. A fastening and fixing structure for astrain wave gearing, comprising: a reduced rotation output element of astrain wave gearing; a fastening friction plate; an output member,wherein the reduced rotation output element and the output member arefastened and fixed in a state in which the fastening friction plate iswedged therebetween, wherein the reduced rotation output element is aflexible externally toothed gear and a reduced rotation is transmittedfrom the flexible externally toothed gear to the output member; thefastening friction plate has a friction plate main body of apredetermined thickness, and engaging protuberances of a predeterminedsize formed at a predetermined pitch on both surfaces of the frictionplate main body; the friction plate main body and the engagingprotuberances are integrally formed by photo-etching into both surfacesof a steel plate material; the engaging protuberances are taperingprotuberances protruding perpendicularly from the surfaces of thefriction plate main body; tips of the engaging protuberances are flatpeak surfaces parallel to the surfaces of the friction plate main body,and side surfaces of the engaging protuberances are concave curvedsurfaces; a cross-sectional shape of the engaging protuberancesorthogonal to a direction of protrusion is circular, square, ortriangular; a hardness of the flexible externally toothed gear is HRC36to HRC50; a hardness of the fastening friction plate is equal to orgreater than HRC55; a thickness of the friction plate main body is 0.1to 0.5 mm, a an arranging pitch of the engaging protuberances is 0.2 to0.5 mm, a maximum diameter or maximum width of peak surfaces of theengaging protuberances is 0.01 to 0.05 mm, and a height of the engagingprotuberances is 1.0 to 1.2 times the maximum diameter or maximum widthof the peak surfaces of the protuberances.
 2. The fastening and fixingstructure for a strain wave gearing and an output member according toclaim 1, wherein the engaging protuberances are arranged in a density of40 to 250 per 10 mm².